279 research outputs found
Microscopic mechanisms of spin-dependent electric polarization in 3d oxides
We present a short critical overview of different microscopic models for
nonrelativistic and relativistic magnetoelectric coupling including the
so-called "spin current scenario", ab-initio calculations, and several recent
microscopic approaches to a spin-dependent electric polarization in 3d oxides.Comment: 8 pages, 3 figure
Electron-conformational transformations in nanoscopic RyR channels govern both the heart's contraction and beating
We show that a simple biophysically based electron-conformational model of
RyR channel is able to explain and describe on equal footing the oscillatory
regime of the heart's cell release unit both in sinoatrial node (pacemaker)
cells under normal physiological conditions and in ventricular myocytes under
Ca SR overload.Comment: 6 pages, 3 figure
Dzyaloshinsky-Moriya antisymmetric exchange coupling in cuprates: Oxygen effects
We revisit a problem of Dzyaloshinsky-Moriya antisymmetric exchange coupling
for a single bond in cuprates specifying the local spin-orbital contributions
to Dzyaloshinsky vector focusing on the oxygen term. The Dzyaloshinsky vector
and respective weak ferromagnetic moment is shown to be a superposition of
comparable and, sometimes, competing local Cu and O contributions. The
intermediate oxygen O Knight shift is shown to be an effective tool to
inspect the effects of Dzyaloshinsky-Moriya coupling in an external magnetic
field. We predict the effect of oxygen weak antiferromagnetism in
edge-shared CuO chains due to uncompensated oxygen Dzyaloshinsky vectors.
Finally, we revisit the effects of symmetric spin anisotropy, in particular,
those directly induced by Dzyaloshinsky-Moriya coupling.Comment: 12 pages, 2 figures, submitted to JET
Disproportionation and electronic phase separation in parent manganite LaMnO_3
Nominally pure undoped parent manganite LaMnO_3 exhibits a puzzling behavior
inconsistent with a simple picture of an A-type antiferromagnetic insulator
(A-AFI) with a cooperative Jahn-Teller ordering. We do assign its anomalous
properties to charge transfer instabilities and competition between insulating
A-AFI phase and metallic-like dynamically disproportionated phase formally
separated by a first-order phase transition at T_{disp}=T_{JT}\approx 750 K.
The unconventional high-temperature phase is addressed to be a specific
electron-hole Bose liquid (EHBL) rather than a simple "chemically"
disproportionated R(Mn^{2+}Mn^{4+})O_3 phase. New phase does nucleate as a
result of the charge transfer (CT) instability and evolves from the
self-trapped CT excitons, or specific EH-dimers, which seem to be a precursor
of both insulating and metallic-like ferromagnetic phases observed in
manganites. We arrive at highly frustrated system of triplet (e_g^2)^3A_{2g}
bosons moving in a lattice formed by hole Mn^{4+} centers. Starting with
different experimental data we have reproduced a typical temperature dependence
of the volume fraction of high-temperature mixed-valent EHBL phase. We argue
that a slight nonisovalent substitution, photo-irradiation, external pressure
or magnetic field gives rise to an electronic phase separation with a
nucleation or an overgrowth of EH-droplets. Such a scenario provides a
comprehensive explanation of numerous puzzling properties observed in parent
and nonisovalently doped manganite LaMnO_3 including an intriguing
manifestation of superconducting fluctuations.Comment: 20 pages, 8 figure
Complex Chiral Modulations in FeGe close to Magnetic Ordering
We report on detailed polarized small-angle neutron scattering on cubic FeGe
in magnetic fields applied either along (transverse) the scattering vector or
parallel (longitudinal)to the neutron beam. The () phase diagrams for all
principal axes contain a segmented -phase region just below the onset of
magnetic order. Hexagonal Bragg-spot patterns were observed across the entire
-phase region for the longitudinal geometry. Scattering intensity was
observed in parts of the A phase for both scattering configurations. Only in a
distinct pocket () vanishing scattering intensity was found in the
transverse geometry.Comment: This paper has been withdrawn by the author due to misunderstanding
with some of the co-author
Dynamical charge inhomogeneity and crystal-field fluctuations for 4f ions in high-Tc cuprates
The main relaxation mechanism of crystal-field excitations in rare-earth ions
in cuprates is believed to be provided by the fluctuations of crystalline
electric field induced by a dynamic charge inhomogeneity generic for the doped
cuprates. We address the generalized granular model as one of the model
scenario for such an ingomogeneity where the cuprate charge subsystem remind
that of Wigner crystal with the melting transition and phonon-like positional
excitation modes. Formal description of R-ion relaxation coincides with that of
recently suggested magnetoelastic mechanism.Comment: 4 page
NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2
We report on {6,7}Li nuclear magnetic resonance measurements of the
spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered
states. Below T about 24 K the NMR lineshape presents a clear signature of
incommensurate (IC) static modulation of the local magnetic field consistent
with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong
phason-like dynamical fluctuations extending well below 24 K. We hypothesize
that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's
staircase" type behavior generic for IC systems. LDA based calculations of
exchange integrals reveal a large in-chain frustration leading to a magnetical
spiral.Comment: 4 pages, 4 figure
Nonbonding oxygen holes and spinless scenario of magnetic response in doped cuprates
Both theoretical considerations and experimental data point to a more
complicated nature of the valence hole states in doped cuprates than it is
predicted by Zhang-Rice model. Actually, we deal with a competition of
conventional hybrid Cu 3d-O 2p state and purely
oxygen nonbonding state with symmetry. The latter
reveals a non-quenched Ising-like orbital moment that gives rise to a novel
spinless purely oxygen scenario of the magnetic response in doped cuprates with
the oxygen localized orbital magnetic moments of the order of tenths of Bohr
magneton. We consider the mechanism of Cu-O 2p transferred orbital
hyperfine interactions due to the mixing of the oxygen O 2p orbitals with Cu 3p
semicore orbitals. Quantitative estimates point to a large magnitude of the
respective contributions both to local field and electric field gradient, and
their correlated character.Comment: 7 pages, 1 figur
Overlap integral for quantum skyrmions
We made use a simplified form for the quantum skyrmion wave function based on
the spin coherent states to obtain the analytical expression for appropriate
overlap integral.Comment: 5 pages, no figure
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